Intraocular pressure is one of the physiological parameters that allows diagnosis and monitoring of eye diseases such as glaucoma. Recently, portable and non-invasive sensing means and methods have been developed in order to measure daily variations of a patient's intraocular pressure, avoiding invasive surgical procedures where sensing means would need to be implanted in a patient's eye. Furthermore, the portability of non-invasive systems has the advantage that patients are no longer required to be immobilized at a hospital or clinic, but that the physiological parameters can now be continuously monitored in daily life situations.
Non-invasive sensing means known in the art usually comprise a sensing device that can be incorporated in a carrier device, such as a contact lens, which will be carried by a patient for monitoring purposes. Furthermore, the non-invasive sensing device can be used in combination with an external monitoring system that can receive and analyze data from the sensing means.
Different types of non-invasive sensing means for contact lenses are known, among which active sensors using miniaturized low power electronics such as microchips, active strain gages and the like, and therefore requiring an energy source. WO 2011/083105 A1 discloses for instance an active sensor comprising concentric strain gages and an associated microprocessor incorporated in a contact lens.
In contrast thereto, purely passive sensors have been developed in order to avoid using an energy source that might cause discomfort to a patient, for instance due to the generation of radiation in close vicinity of or even in direct contact with the patient's eye. A passive sensor is known from EP 2 412 305 A1, disclosing a portable physiological parameter monitoring system comprising a resonant LC circuit incorporated in a soft contact lens, wherein the resonant LC circuit responds to an external magnetic field generated by a complementary portable device, as known from instance from EP 2 439 580 A1, as well as a base station for analyzing the data acquired by the portable device. This type of passive sensor is known to rely on variations of the resonance frequency of the LC circuit incorporated in the contact lens as a function of variations of the intraocular pressure, as the latter should affect the shape of the surface of the eye and, consequently, also of the soft contact lens resting thereon. In turn, deformations of the soft contact lens should modify a capacitance of the resonant circuit.
However, the integration of sensors, passive or active, in soft contact lenses has been found to be more complex and more expensive than expected, preventing thus far a commercialization of portable intraocular pressure monitoring systems. A recurrent problem is that sensors are usually manufactured flat and subsequently bent to adopt the spherical cap shape of the over-molded lens, which has been found to create deformed areas in the final lens, for instance rippled edges, and sometimes also misalignments between the electrical components of the sensor. Thus, further to not being comfortable for wearing the lens, these deformations prevent a proper flat placement of the lens against the surface of the eye. As a consequence, the necessary sensitivity of the system to deformations of the surface of the eye cannot be reached.
It is also known from WO 2009/111726 A2 to provide surface deformation sensor comprising a contact lens formed by an external rigid layer and an internal soft layer bounded together at their edge, with a gap between the rigid and the soft layers, wherein a resonant LC circuit is split into components integrated in the rigid layer and components integrated in the soft layer, with electrical connection means therebetween. In particular, WO 2009/111726 A2 discloses a resonant LC circuit formed by an inductive coil and a sensing capacitor, wherein the inductive coil and an upper electrode of the capacitor are included in the rigid layer and electrically connected to a lower electrode included in the soft layer.
However, the fabrication of surface deformation sensor comprising such “multilayered hybrid” contact lenses requires various complex steps of integrating circuit components both in the rigid and in the soft layers, as well as the integration of a mechanism for electrically connecting the two layers. Furthermore, as they still include circuit components in the soft layer, such surface deformations sensors can also face the problems of unwanted ripples in the soft layer, and therefore the deformation of the soft layer may not reflect the actual deformation of the surface of the eye.
Thus, an objective of the present invention is to provide an improved physiological parameter monitoring device compared to intraocular pressure monitoring devices and surface deformation sensors known in the art. An objective of the present invention is also to provide an improved physiological parameter monitoring system using a multilayered contact lens and a passive sensor, which prevents or even avoids the aforementioned problems. Furthermore, common requirements of comfort of wearing and, as much as possible, unimpaired vision of the subject wearing the contact lens with integrated passive sensor should also be respected. Finally, an objective of the present invention is also to provide a physiological parameter monitoring device that improves the placement of the contact lens against the surface of an eye and the responsiveness of the passive sensor to surface deformations.